With the rapid penetration of wireless communication technology in the Internet of Things (IoT), the ability to sense and respond to physical distance between people and objects, and between objects themselves, has become crucial for enhancing device intelligence and the human interaction experience. When a smart refrigerator senses a user's approach and automatically illuminates the screen to display the fruits and vegetables inside, when an access control system senses the approach of an authorized person and automatically opens the door, or when an office senses the departure of all staff and automatically turns off the lights, a whole new range of possibilities emerges.
The Channel Sounding feature supported in the BLE 6.0 specification is one of the excellent options for developers to realize these new possibilities. It not only injects true distance perception capabilities into IoT devices, but also reshapes the distance perception logic between people and objects, and between objects and objects through its advantages such as security, reliability, low power consumption, strong anti-interference ability, and "centimeter-level" perception accuracy. It is the key to unlocking the intelligence of all things.
The Bluetooth Special Interest Group (SIG) stated that the Bluetooth channel detection function mainly uses two proven ranging methods, namely phase-based ranging (PBR) and round-trip time (RTT), to achieve secure and precise ranging between Bluetooth-connected devices. It can be widely used in application scenarios such as indoor positioning, distance detection and proximity sensing.
For example, the HM-BT2401DA is a channel sounding module independently developed by HOPERF based on the high-performance BLE6.0 chip. It supports two ranging roles: initiator (want to calculate the distance from itself to the target device) and reflector (reflector: respond to the initiator). It supports dual antenna paths and can quickly realize wireless connection and ranging of initiator (Initiator) and reflector (Reflector) through AT commands. The external MCU resource usage is low and the development process is simple.
As shown in the figure above, the HM-BT2401DA supports RTT (round-trip time) and PBR (phase-based ranging) modes. During channel detection, the initiator sends a carrier signal or data packet on one of the 72 designated 2.4 GHz physical channels. The reflector responds by sending the carrier signal or data packet back to the initiator. After determining the round-trip time of the data packet and the phase difference between carrier signals of different frequencies, the initiator runs a specific distance measurement algorithm to determine the exact distance between the two and reports the calculated result to the MCU via the serial port.
The initiator device is responsible for actively initiating ranging requests, collecting data, and calculating distances. During a single ranging process, it interacts point-to-point with only one reflector device. The reflector device is responsible for passively responding to the initiator's signals and returning raw data. During a single ranging process, it interacts point-to-point with only one initiator device.
It is worth mentioning that, thanks to key functional features such as high-performance 2.4 GHz radio frequency, low current consumption, AI/ML hardware accelerator and security vault, the HM-BT2401DA can also be used in low-power Bluetooth and mesh wireless connection communication solutions; IoT device manufacturers can integrate this module to create smart, powerful and energy-saving products that are protected from remote and local network attacks.
To fully verify the channel detection capabilities of the HM-BT2401DA, HOPERF Laboratory conducted multiple field tests. In PBR (Phase-Based Ranging) mode, the HM-BT2401DA has achieved a positioning accuracy of approximately 50cm within a range of 10 meters. It can be widely used in warehouse management, item tracking, pet tracking and other fields in indoor environments.
HM-BT2401DA channel detection function test data (PBR mode)
Test conditions: Indoor environment, no obstacles between modules, using PBR mode at a height of 1 meter from the ground.
With this centimeter-level distance perception capability, the HM-BT2401DA is expected to bring a host of innovative interactive applications to industries such as industry, home, and retail . Examples include keyless entry for cars and homes , geofencing-based security policies that unlock doors for authorized users as they approach, and alarms that sound if users remain in sensitive areas for too long. Bluetooth mice, keyboards, and game controllers can automatically switch between active and inactive states based on their proximity to smartphones, tablets, or laptops .
Looking ahead, as BLE channel detection functions continue to be optimized towards "low power consumption, high precision, and high reliability," its distance perception capabilities will further blur the boundaries of interaction between people and devices, and accurately match people's needs for "near-field interaction, long-term deployment, and multi-device collaboration," enabling IoT devices to change from "requiring manual operation" to "responding upon approach," making production more efficient and life more convenient.
